The polyphenylene ethers are known and described in numerous publications, including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875; and Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358, all incorporated herein by reference. The high molecular weight polyphenylene ethers are high performance engineering thermoplastics having relatively high melt viscosities and softening points, i.e., in excess of 275.degree. C. They are useful for many commercial applications requiring high temperature resistance and can be formed into films, fibers and molded articles.
While possessing the above described desirable properties, it is also known that certain of the properties of the polyphenylene ethers are undesirable for some commercial uses. For example, parts molded from polyphenylene ethers have low impact strength because they are somewhat brittle. In addition, the relatively high melt viscosities and softening points are considered a disadvantage for many uses. Films and fibers can be formed from polyphenylene ethers on a commercial scale using solution techniques, but melt processing is commercially unattractive because of the required high temperatures needed to soften the polymer and the problems associated therewith such as instability and discoloration. Such techniques also require specially designed process equipment to operate at elevated temperatures. Molded articles can be formed by melt processing techniques, but, again, the high temperatures required are undesirable.
It is known in the art that the properties of the polyphenylene ethers can be materially altered by forming compositions with other polymers. For example, Finhlot, U.S. Pat. No. 3,379,792 discloses that flow properties of polyphenylene ethers are improved by preparing a composition thereof with from aboutt 0.1 to 25 parts by weight of a polyamide. In Gowan, U.S. Pat. No. 3,361,851, polyphenylene ethers are formed into compositions with polyolefins to improve impact strength and resistance to aggressive solvents. In Cizek, U.S. Pat. No. 3,383,435, incorporated herein by reference, Fox, U.S. Pat. No. 3,356,761, and Bostick et al, French Pat. No. 1,586,729, there are provided means to simultaneously improve the melt processability of the polyphenylene ethers and upgrade many properties of polystyrene resins. These patents disclose that polyphenylene ethers and vinyl materials, e.g., blended or grafted polystyrene resins, including many modified polystyrenes, are combinable in all proportions to provide compositions having many properties improved over those of either of the components. This invention provides compositions of the type disclosed broadly in such prior art, but with unexpectedly high impact strength.
Preferred embodiments of the Cizek patent are compositions comprising a rubber modified high-impact polystyrene and a poly(2,6-dialkyl-1,4-phenylene)ether. Such compositions are important commercially because they provide both an improvement in the melt processability of the polyphenylene ether and an improvement in the impact resistance of parts molded from the compositions. Furthermore, such compositions of the polyphenylene ether and the rubber modified high-impact polystyrene may be custom formulated to provide pre-determined properties ranging between those of the polystyrene resin and those of the polyphenylene ether by controlling the ratio of the two polymers. The reason for this is that the Cizek compositions exhibit a single set of thermodynamic properties rather than the two distinct sets of properties, i.e., one for each of the components of the composition, as is typical with compositions or blends of the prior art.
The preferred embodiment of the Cizek patent is disclosed to comprise a poly(2,6-dimethyl-1,4-phenylene)ether and a rubber modified high-impact polystyrene (identified in Example 7 as Lustrex HT 88-1 of Monsanto Chemical Company). It is known in the art that Monsanto HT-88 high impact polystyrene contains an elastomeric rubber phase dispersed through a polystyrene matrix and that the particle size of the dispersed elastomer ranges from 2 to 10 microns with an average of 4 to 6 microns. This is shown, for example, in the photomicrograph in Vol. 19, Encyclopedia of Chemical Technology, 2nd Edition, 1969, page 94, FIG. 2(b). Moreover, the prior art high impact rubber modified polystyrenes comprise about 12-21% by weight of an elastomeric gel phase dispersed in a polystyrene matrix and, in Monsanto HT-88, a typical sample had a 20.7% rubber gel content. This is shown, e.g., in Table 3 of Vol. 13, Encyclopedia of Polymer Science and Technology, 1970, p. 401 et seq. In addition, it is known that rubber in high impact polystyrene like Monsanto HT-88 comprised a butadiene-based polymer and that the butadiene units in such polymers had a typical, high trans microstructure. Thus the preferred embodiment of the Cizek patent, which was disclosed to have a notched Izod impact strength ranging from 1.05 to 1.5 ft.-lbs./in. notch (Standard method, ASTM D-256) comprised a polyphenylene ether and a rubber modified high-impact polystyrene resin having a dispersed rubber gel phase with average particle size of about 4 to 6 microns, the polystyrene containing less than 21% by weight of a dispersed rubber gel phase, and the rubber being a butadiene-based polymer in which the microstructure of the polybutadiene was largely trans-1,4.
the Cizek patent claims compositions which dominate those of this application and its copending parents, although the present compositions are patentably distinguishable therefrom.
In particular, in copending application, Serial No. 122,079, it is disclosed that such compositions having a rubber particle size range averaging in the sub-2 micron range have higher impact strengths than the compositions specifically disclosed by Cizek. In copending application, Ser. No. 139,270 it is disclosed that such compositions in which the rubber is of a predominantly cis-1,4 microstructure have higher impact strengths than the compositions specifically disclosed by Cizek. In copending application, Serial No. 139,215, it is disclosed that such compositions in which the rubber gel content on a polyphenylene-free basis exceeds 22% by weight have higher impact strengths than the compositions specifically disclosed by Cizek.
Moreover, data are presented which demonstrate that the compositions of the three said copending applications are also patentably distinct from one another because
(i) if the rubber particle size is maintained in a sub-2 micron average range while the cis-content is held below 50% and the rubber gel phase is held below 22%, ductile impact strength (Gardner) at room temperature and gloss both are better than that of a composition in which the particle size is greater than 2 microns; PA1 (ii) if the rubber is &gt;90% cis-1,4 polybutadiene while the average particle size is held above 2 microns and the rubber gel phase content is held below 22%, brittle impact strength (Izod) at room temperature is better than that of a composition in which the microstructure of the cis-1,4 polybutadiene is less than 50%; and PA1 (iii) if the rubber gel phase content is above 22% by weight on a polyphenylene ether-free basis while the cis-1,4 content is held below 50% and the rubber particle size is kept above 2 microns, average, the ductile impact strength (Gardner) at room temperature is improved and the percent retention of brittle impact (Izod) at -40.degree. C. is better than that of a composition in which the rubber gel phase content is less than 22%.
The present compositions are patentably distinguishable over those specifically disclosed in Cizek patent because they have higher impact strengths. Moreover, they are patentably distinguishable over the compositions of the copending parent applications because the present compositions have a higher gloss, and a substantially higher brittle impact strength (Izod) at -40.degree. C.
In addition to the enhanced impact strength, the present compositions have improved surface appearance, especially gloss, and much greater resistance to aggressive solvents, such as gasoline, in comparision with all other polyphenylene etherstyrene resin compositions of the prior art.